In the prior art conduits for carrying cables, e.g., fiber optic, electrical, etc., have been connected by an expansion joint (coupling) to accommodate changing temperatures. Such expansion joints basically comprise two members, namely a collar and a cap, which are threadedly secured together. The collar is a cylindrical member having one end at which there is disposed a female threaded opening. That threaded opening is arranged to receive the trailing end of one conduit, e.g., a leading conduit. The cap is threadedly secured onto the collar and includes a smooth, i.e., non-threaded, opening for receiving the leading end of the next, e.g., trailing, conduit. Since the leading end of the trailing conduit is not threadedly engaged by any portion of the coupling it can thus slide longitudinally through the opening in the coupling's cap.
It has been found that when such couplings are used in application wherein the conduits are supported above the ground, e.g., where they cross bridges, overpasses, etc., the conduits have a tendency to become disconnected. Such disconnections typically result from vibrations which are transmitted to the structure supporting the conduits and expansion joint coupling. In particular, where the conduits are supported by rollers or some other means to enable the conduits to move longitudinally, loosening, if not total disconnection, commonly occurs. In this regard since the trailing conduit can slide longitudinally within the cap of the coupling (it is not threaded in that cap) it is free to rotate about its longitudinal axis, whereupon it may become unthreaded from the threaded collar of the trailing coupling.